Process for fabricating semiconductor laser emitting apparatus

ABSTRACT

In the fabrication of a semiconductor laser emitting apparatus which emits laser beams having two different wavelengths, surface steps of the laminate film which is formed so as to cover the first semiconductor laser emitting device and constitutes the second semiconductor laser emitting device, is removed, so that processing with high precision is realized. A process for fabricating a semiconductor laser emitting apparatus comprising first and second semiconductor laser emitting devices, which are formed on a substrate and respectively emit laser beams having different wavelengths, the process comprising: stacking a ternary-system compound semiconductor on the substrate in a region in which the first semiconductor laser emitting device is to be formed, to thereby form a first laminate; forming a second laminate comprised of a quaternary-system compound semiconductor on the substrate so that the second laminate covers the first laminate; planarizing the surface of the second laminate so that the surface of the first laminate is exposed to the outside; forming current injection regions in the cladding layer; forming a current constriction region; and separating the first laminate from the second laminate, to thereby form a space between the laminates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for fabricating asemiconductor laser emitting apparatus. More particularly, the presentinvention is concerned with a process for fabricating a semiconductorlaser emitting apparatus which emits laser beams having two differentwavelengths.

2. Description of the Related Art

A conventional process for fabricating a semiconductor laser emittingapparatus which emits laser beams having two different wavelengths isdescribed below with reference to diagrammatic cross-sectional views ofFIGS. 2A to 2H illustrating the fabrication process.

As shown in FIG. 2A, on an n-type substrate 110 comprised of GaAs, afirst n-type buffer layer 131 comprised of GaAs, a first n-type claddinglayer 132 comprised of AlGaAs, a first active layer (having a multiplequantum well (MQW) structure having an oscillation wavelength of 780 nm)133, a first p-type cladding layer 134 comprised of AlGaAs, and a firstp-type cap layer 135 comprised of GaAs are stacked on one another inthis order by a metal organic vapor phase epitaxial growth (hereinafter,frequently referred to simply as “MOVPE”) method.

Then, as shown in FIG. 2B, a resist film (not shown) is formed so thatit covers a region 121 in which a first semiconductor laser emittingdevice is to be formed (first semiconductor laser emitting deviceformation region 121), and the layers of from the first p-type cap layer135 to the first n-type cladding layer 132, excluding the portioncorresponding to the first semiconductor laser emitting device formationregion 121, are removed using the above resist film as-a mask by a wetetching process, such as a sulfuric acid system non-selective etchingprocess and a hydrofluoric acid (HF) system selective etching processfor AlGaAs, to thereby form, in the first semiconductor laser emittingdevice formation region 121, a first laminate 123 in which the firstp-type cap layer 135, the first p-type cladding layer 134, the firstactive layer 133, and the first n-type cladding layer 132 are stacked onone another.

Subsequently, as shown in FIG. 2C, on the first n-type buffer layer 131,a second n-type buffer layer 136 comprised of InGaP, a second n-typecladding layer 137 comprised of AlGaInP, a second active layer (having amultiple quantum well (MQW) structure having an oscillation wavelengthof 650 nm) 138, a second p-type cladding layer 139 comprised of AlGaInP,and a second p-type cap layer 140 comprised of GaAs are stacked on oneanother in this order by a MOVPE method so that they cover the firstlaminate 123.

Then, as shown in FIG. 2D, a resist film (not shown) is formed so thatit covers a region 122 in which a second semiconductor laser emittingdevice is to be formed (second semiconductor laser emitting deviceformation region 122). The layers of from the second p-type cap layer140 to the second n-type buffer layer 136, excluding the portioncorresponding to the second semiconductor laser emitting deviceformation region 122, are removed using the above resist film as a maskby a wet etching process, such as a sulfuric acid system etching processfor a cap layer and a phosphoric acid and hydrochloric acid systemselective etching process for a quaternary-system compoundsemiconductor, and a hydrochloric acid system separation etchingprocess, to thereby form, in the second semiconductor laser emittingdevice formation region 122, a second laminate 124 in which the secondn-type buffer layer 136, the second n-type cladding layer 137, thesecond active layer 138, the second p-type cladding layer 139, and thesecond p-type cap layer 140 are stacked on one another. As a result, thefirst laminate 123 and the second laminate 124 are separated from eachother.

Subsequently, as shown in FIG. 2E, insulating films 125 are formed onthe first laminate 123 and the second laminate 124 so that they coverportions which are to be current injection regions, and then, forforming a stripe structure which is to be a current constrictionstructure of a gain guide type, from surfaces of the first p-type caplayer 135 and the second p-type cap layer 140 to halfway portions of thefirst p-type cladding layer 134 and the second p-type cladding layer 139are respectively processed in a ridge form in a certain depth of thefirst p-type cladding layer 134 and the second p-type cladding layer 139by an etching process using the insulating films 125 as a mask.

Then, as shown in FIG. 2F, an n-type layer 141 comprised of, forexample, GaAs is allowed to selectively grow on the compoundsemiconductor layer, so that it implants the portions etched in a ridgeform in the first p-type cladding layer 134 and the second p-typecladding layer 139.

Then, the insulating films 125 are removed by an etching process.Subsequently, as shown in FIG. 2G, a resist film (not shown) is formedso that it covers only the portions of the n-type layer 141 formed onthe first laminate 123 and the second laminate 124, and then, the n-typelayer 141 is removed by an etching process using the above resist filmas a mask so that the only portions of the n-type layer 141 on the firstlaminate 123 and the second laminate 124 remain.

Then, as shown in FIG. 2H, the resist film is removed. Further, a firstp-type electrode 143 and a second p-type electrode 144 respectivelyconnected to the first p-type cap layer 135 and the second p-type caplayer 140 are formed from, for example, a Ti/Pt/Au laminate, and ann-type electrode 151 connected to the n-type substrate 110 is formedfrom, for example, a AuGe/Ni/Au laminate.

However, in the step for separating the first semiconductor laseremitting device comprising the first laminate from the secondsemiconductor laser emitting device comprising the second laminate, anexposure step for a resist film which serves as a mask for etching isinevitably performed in a state such that the surface step of the layerdirectly under the resist film is large. Therefore, it has beendifficult to achieve the patterning for resist with precision.

In addition, it is necessary that the step for separating the firstsemiconductor laser emitting device comprising the first laminate fromthe second semiconductor laser emitting device comprising the secondlaminate by an etching process, and the step for separating the n-typelayer which constitutes the current constriction layer by an etchingprocess be separately conducted in two different separation steps.Therefore, a burden on the process has been large.

SUMMARY OF THE INVENTION

The present invention is a process for fabricating a semiconductor laseremitting apparatus which has been made for solving the above-mentionedproblems accompanying the prior art.

The process of the present invention is a process for fabricating asemiconductor laser emitting apparatus comprising a first semiconductorlaser emitting device and a second semiconductor laser emitting device,which are formed on a substrate and respectively oscillate laser beamshaving different wavelengths, the process comprising the steps of:stacking on the substrate a compound semiconductor layer whichconstitutes the first semiconductor laser emitting device, to therebyform a first laminate; removing the first laminate so that the portionof the first laminate in a region in which the first semiconductor laseremitting device is to be formed remains; stacking on the substrate acompound semiconductor layer which constitutes the second semiconductorlaser emitting device, to thereby form a second laminate; removing thesecond laminate formed on the first laminate, to thereby expose asurface of the first laminate to the outside and planarize a surface ofthe second laminate; forming current injection regions in a ridge formin the first and second laminates, respectively; selectively forming acurrent constriction layer on the portion of the first and secondlaminates other than the current injection regions; and forming a spacein the current constriction layer and between the first laminate and thesecond laminate, to thereby separate the first laminate from the secondlaminate.

The process for fabricating a semiconductor laser emitting apparatus ofthe present invention includes a step for removing the second laminateformed on the first laminate, to thereby expose the surface of the firstlaminate to the outside and planarize the surface of the secondlaminate. Therefore, in the subsequent step for separating the firstlaminate from the second laminate, to thereby form a space between thelaminates, an exposure step for a resist film which serves as a mask foretching can be performed in a state such that the surface of the layerdirectly under the resist film is planarized, so that patterning forresist can be conducted with high precision, enabling the separation tobe achieved with high precision.

In addition, in the process of the present invention, the step forseparating the first laminate from the second laminate, to thereby forma space between the laminates, and the step for separating the currentconstriction layer by an etching process are conducted in the sameseparation step. Therefore, a burden on the process can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the presentinvention will be apparent to those skilled in the art from thefollowing description of the presently preferred exemplary embodimentsof the invention taken in connection with the accompanying drawings, inwhich:

FIGS. 1A to 1H are diagrammatic cross-sectional views illustrating aprocess for fabricating a semiconductor laser emitting apparatusaccording to one embodiment of the present invention;

FIGS. 2A to 2H are diagrammatic cross-sectional views illustrating aconventional process for fabricating a semiconductor laser emittingapparatus; and

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The semiconductor laser emitting apparatus according to one embodimentof the present invention is described below with reference to thediagrammatic cross-sectional views of FIGS. 1A to 1H illustrating thefabrication process. The thickness of layers is not limited to thatshown in the drawings, but may be varied within the scope of theinvention.

As shown in FIG. 1A, a first n-type buffer layer 12 is formed on asubstrate 10 by an epitaxial growth method, such as a MOVPE method.Then, on the first n-type buffer layer 12, a first n-type cladding layer13 as a first conductive cladding layer, a first active layer 14 havinga multiple quantum well (MQW) structure having an oscillation wavelengthof 780 nm, a first p-type cladding layer 15 as a second conductivecladding layer, and a first p-type cap layer 16 are stacked on oneanother in this order, to thereby form a first laminate 17. In thepresent embodiment, the first conductive cladding layer is an n-typecladding layer and the second conductive cladding layer is a p-typecladding layer. However, any other modification may be available withinthe scope of the invention. As the substrate 10, for example, an n-typeGaAs substrate is used, and the first n-type buffer layer 12 is formedfrom, for example, an n-type GaAs layer. The first n-type cladding layer13 is formed from, for example, an n-type AlGaAs layer, and the firstp-type cladding layer 15 is formed from, for example, a p-type AlGaAslayer. The first p-type cap layer 16 is formed from, for example, ap-type Gays layer. Guide layers may be formed between the first activelayer 14 and the first n-type cladding layer 13 and between the firstactive layer 14 and the first p-type cladding layer 15.

Then, as shown in FIG. 1B, a resist film (not shown) is formed so thatit covers a region 11 in which a first semiconductor laser emittingdevice is to be formed (first semiconductor laser emitting deviceformation region 11), and then, the layers of from the first p-type caplayer 16 to the first n-type cladding layer 13, excluding the portioncorresponding to the first semiconductor laser emitting device formationregion 11, are removed using the above resist film as a mask by a wetetching process, such as a sulfuric acid system non-selective etchingprocess and a hydrofluoric acid (HF) system selective etching processfor AlGaAs. As a result, in the first semiconductor laser emittingdevice formation region 11, the first laminate 17 in which the firstn-type cladding layer 13, the first active layer 14, the first p-typecladding layer 15, and the first p-type cap layer 16 are stacked on oneanother in this order remains.

Subsequently, as shown in FIG. 1C, for example, on the first n-typebuffer layer 12, a second n-type buffer layer 22, a second n-typecladding layer 23 as a first conductive layer, a second active layer 24having a multiple quantum well (MQW) structure having an oscillationwavelength of 650 nm, a second p-type cladding layer 25 as a secondconductive layer, and a second p-type cap layer 26 are stacked on oneanother in this order by an epitaxial growth method, for example, aMOVPE method, to thereby form a second laminate 27. The second n-typebuffer layer is formed from, for example, an n-type InGaP layer, and thesecond n-type cladding layer 23 is formed from, for example, an n-typeAlGaInP layer. The second p-type cladding layer 25 is formed from, forexample, a p-type AlGaInP layer, and the second p-type cap layer 26 isformed from, for example, a p-type GaAs layer.

Then, a planarization film (not shown) is formed on the second laminate27 from, for example, a resist, and then, an etching process forplanarization (etch back) is performed so that the uppermost surface ofthe first laminate 17 is exposed to the outside. As a result, as shownin FIG. 1D, the second laminate 27 comprising the second n-type bufferlayer 22, the second n-type cladding layer 23, the second active layer24, the second p-type cladding layer 25, and the second p-type cap layer26 is planarized, and the uppermost surface of the first laminate 17 isexposed to the outside.

Next, as shown in FIG. 1E, insulating films 31 are formed on the firstlaminate 17 and the second laminate 27 so that they cover portions whichare to be current injection regions.

Then, as shown in FIG. 1F, for forming a stripe structure which is to bea current constriction structure of a gain guide type, for example, fromsurfaces of the first p-type cap layer 16 and the second p-type caplayer 26 to halfway portions of the first p-type cladding layer 15 andthe second p-type cladding layer 25 are respectively processed in aridge form in a certain depth of the first p-type cladding layer 15 andthe second p-type cladding layer 25 by an etching process using theinsulating films 31 as a mask. The resultant regions processed in aridge form become current injection regions 32, 33. By changing thedepth d for etching, the stripe structure can be of either a gate guidetype or an index guide type.

Subsequently, as shown in FIG. 1G, on the exposed first and secondlaminates 17, 27, for example, an n-type layer is allowed to selectivelygrow by a selective growth method using the insulating films 31 as amask, to thereby form a current constriction layer 34. In thisembodiment, the current constriction layer 34 is formed from, forexample, an n-type GaAs layer.

Then, the insulating films 31 are removed by an etching process.Subsequently, as shown in FIG. 1H, a resist film (not shown) is formedso that it covers the current constriction layer 34, the first andsecond p-type cap layers 16, 26 and the like, and then, the resist filmis subjected to patterning by a lithography technique, to thereby form aresist film (not shown) which covers the first semiconductor laseremitting device formation region 11 and a second semiconductor laseremitting device formation region 21 in which first and secondsemiconductor laser emitting devices are to be respectively formed.

The portion of the second laminate 27 up to the second n-type bufferlayer 22, excluding the portion corresponding to the secondsemiconductor laser emitting device formation region 21, is removedusing the above resist film as a mask by a wet etching process, such asan etching process for the current constriction layer 34 using anammonia etching liquid and a selective etching process for aquaternary-system compound semiconductor using a phosphoric acid andhydrochloric acid etching liquid, and a hydrochloric acid systemseparation etching process. As a result, a space 35 is formed between afirst semiconductor laser emitting device 3 mainly comprised of thefirst laminate 17 and a second semiconductor laser emitting device 5mainly comprised of the second laminate 27, so that the firstsemiconductor laser emitting device 3 and the second semiconductor laseremitting device 5 are separated from each other.

Then, the resist film is removed. Further, a first p-type electrode 18connected to the first p-type cap layer 16 is formed from, for example,a Ti/Pt/Au laminate, and a second p-type electrode 28 connected to thesecond p-type cap layer 26 is formed from, for example, a Ti/Pt/Aulaminate. Furthermore, an n-type electrode 51 connected to the substrate10 is formed from, for example, an AuGe/Ni/Au laminate.

Thus, a semiconductor laser emitting apparatus 1 having mounted on thesame chip the first semiconductor laser emitting device 3 which mainlycomprises the first laminate 17 and the second semiconductor laseremitting device 5 which mainly comprises the second laminate 27 iscompleted.

The process for fabricating the semiconductor laser emitting apparatus 1contains a step for removing the second laminate 27 formed on the firstlaminate 17, to thereby expose the surface of the first laminate 17 tothe outside and planarize the surface of the second laminate 27.Therefore, in the subsequent step for separating the first laminate 17from the second laminate 27, to thereby form the space 35 between thelaminates, an exposure step for the resist film (not shown) which servesas a mask for etching can be performed in a state such that the surfaceof the layer directly under the resist film is planarized, so thatpatterning for resist can be conducted with high precision, enabling theseparation to be achieved with high precision.

As mentioned above, the process for fabricating a semiconductor laseremitting apparatus of the present invention includes a step for removingthe second laminate formed on the first laminate, to thereby expose thesurface of the first laminate to the outside and planarize the surfaceof the second laminate. Therefore, in the subsequent step for separatingthe first laminate from the second laminate, to thereby form a spacebetween the laminates, an exposure step for a resist film which servesas a mask for etching can be performed in a state such that the surfaceof the layer immediately under the resist film is planarized, so thatpatterning for resist can be conducted with high precision. Thus, it ispossible to separate the ternary-system compound semiconductor regionfrom the quaternary-system compound semiconductor region with highprecision. In addition, in the process of the present invention, thestep for separating the first laminate from the second laminate, tothereby form a space between the laminates, and the step for separatingthe insulating layer which constitutes the current constriction layer byan etching process are conducted in the same separation step. Therefore,a burden on the process can be reduced.

What is claimed is:
 1. A process for fabricating a semiconductor laseremitting apparatus comprising a first semiconductor laser emittingdevice and a second semiconductor laser emitting device, which areformed on a substrate and respectively oscillate laser beams havingdifferent wavelengths, said process comprising the sequential steps of:stacking on said substrate a compound semiconductor layer whichconstitutes said first semiconductor laser emitting device to form afirst laminate; removing said first laminate so that a portion of saidfirst laminate in a region in which said first semiconductor laseremitting device is to be formed remains by covering said portion of saidfirst laminate with a film; stacking on said substrate and said firstlaminate a compound semiconductor layer which constitutes said secondsemiconductor laser emitting device to form a second laminate; removingsaid second laminate formed on said first laminate to expose a surfaceof said first laminate and planarize said second laminate, so as to notseparate the first and second laminates; forming a current injectionregion in a ridge form on said first and second laminates; selectivelyforming a current constriction layer on a portion of said first andsecond laminates other than said current injection regions on said firstand second laminates; and forming a space in said current constrictionlayer and between said first second laminates, thereby separating saidfirst laminate from said second laminate.
 2. A process for fabricating asemiconductor laser emitting apparatus, comprising the sequential stepsof: forming a first laminate on a substrate by stacking a compoundsemiconductor layer which constitutes a first semiconductor laseremitting device; selectively removing said first laminate in a region inwhich said first semiconductor laser emitting device is to be formed;forming a second laminate on said substrate and said first laminate bystacking a compound semiconductor layer which constitutes a secondsemiconductor laser emitting device; covering said second laminate witha film and selectively removing said second laminate formed on saidfirst laminate to expose an uppermost surface of said first laminate andto planarize said second laminate formed on said substrate, so as to notseparate the first and second laminates; forming a current injectionregion on each of said first and second laminates; selectively forming acurrent constriction layer on a portion of said first and secondlaminates other than said current injection regions; and forming a spacein said current constriction layer and between said first laminate andsaid second laminate to separate said first laminate from said secondlaminate.